This application addresses broad Challenge Area (06) Enabling Technologies and specific Challenge Topic, 06-CA-116: Physical Sciences and Cellular Mechanics. We will develop analytical imaging capabilities with complementary nanoparticle probes to measure the viscoelastic properties of cells and tissues in a noninvasive manner. These capabilities will be applied toward understanding biomechanical factors on tumor growth dynamics. Near-infrared (NIR) absorbing Au nanoparticles with magnetic cores will serve as multimodal contrast agents for multiphoton imaging and for magnetomotive optical coherence tomography (MM-OCT) and elastography (MM-OCE), to characterize viscoelastic changes in tumor cells and tissues as a function of their development. Tumor cells will be laden with nanoprobes and cocultured with fibroblasts or macrophages for in vitro multimodal imaging with MM-OCE. Tumor xenografts will also be grown in mice from nanoprobe-laden tumor cells, then excised for ex vivo imaging with results collated with conventional metrics of tumor development (i.e., visual inspection and histology). We anticipate this approach can reveal critical biomechanical differences in the development of invasive carcinomas, in which cells undergo transformations from turgid states with high tensile strength to plastic and deformable states associated with migration and extravasation. Our Specific Aims are as follows: 1) Construction of an integrated optical platform for optical coherence tomography (OCT) and elastography (OCE), for noninvasive imaging of tumor tissues with cellular resolution; 2) Fabrication of nanoprobes that combine plasmon resonance with magnetomotive activity, to generate unique NIR signatures for 3D imaging and elastography; 3) Optimization and deployment of the multimodal imaging platform for simultaneous structural imaging and viscoelastic profiling of nanoprobe-laden tumor cells and excised tumor tissues.